This invention relates to a probe-test method and also to a prober.
More particularly, the present invention relates to a probe-test method for determining certain electric characteristics of an object of examination and also to a prober to be used for such a test. While a prober for determining certain electric characteristics of integrated circuits (hereinafter referred to as IC chips) that are arranged on a semiconductor wafer (hereinafter referred to simply as wafer) may represent a typical and specific application of the present invention, the present invention is not limited thereto and a prober according to the invention may find applications in examining various electronic elements and devices for certain electric characteristics by means of a probe.
FIG. 6 of the accompanying drawings schematically illustrates known prober to be used for examining IC chips.
The prober 10 comprises a loader chamber 11 from which wafers contained in respective cassettes are taken out one by one and transferred, a prober chamber 12 for examining the wafers W transferred from the loader chamber 11, a controller 13 for controlling the prober chamber 12 and the loader chamber 11 and a display unit 14 that also operates as a control panel for driving the controller 13.
In the loader chamber 11, a fork 15 is rotatably fitted to a rotary shaft for transferring a wafer W from the inside of a cassette C. The fork 15 is horizontally extensible/retractable and also rotatable to face oppositely in order to take out wafers W in the cassette C on a one by one basis and transfer them to the prober chamber 12. A sub-chuck 16 is arranged near the fork 15 for pre-aligning wafers W. More specifically, the sub-chuck receives a wafer W from the fork 15, rotates it in the sense of .theta. in order to make it face oppositely and then pre-align the wafer W by referring to its orientation flat.
In the prober chamber 12, there are provided a main chuck 17 for carrying a wafer w therein, an aligning means 20 and a probe card. The main chuck 17 is adapted to be driven in the X- and Y-directions of the prober by means of X- and Y-stages 18 and 19 and also in the Z- and .theta.-directions by means of a built-in drive mechanism.
The aligning means 20 comprises an alignment bridge having a first image pick-up means (e.g., a CCD camera) 21 for shooting the wafer W in position to pick up an image thereof, a pair of guide rails 23, 23 for reciprocating the alignment bridge 22 along the Y-direction and a second image pick-up means (not shown, e.g, a CCD camera) fitted to the main chuck 17.
A tester head (not shown) is arranged on the upper surface of the probe card and connected thereto by means of a connection ring (not shown). A test signal transmitted from the tester that comprises the prober is sent to electrodes of the IC chip being examined by way of the tester head, the connection ring and the probes of the probe card and the output signal of the IC chip representing the test result is sent back to the tester by way of the same signal route. The tester is adapted to determine certain electric characteristics of the IC chip on the basis of the signal representing the test result.
For testing a wafer W, the fork 15 takes a wafer W out of the cassette C in the loader chamber 11. The wafer W is then pre-aligned by the sub-chuck 16 on its way of being transferred to the prober chamber 12 and moved onto the main chuck 17 in the prober chamber 12. Then, the alignment bridge 22 moves over the main chuck 17 until the wafer W is placed to a position right below the first image pick-up means 21 of the alignment bridge 22, where the first image pick-up means 21 and the second image pick-up means of the main chuck 17 cooperate for the alignment of the wafer W on the main chuck 17. The main chuck 17 is adapted to move in the X- and Y-directions for indexing the wafer W for each test and then move upward in the Z-direction until the wafer W comes into physical contact with the probes. Then, the main chuck 17 is driven upward excessively further in the Z-direction to make the electrode pads of the IC chip on the wafer W electrically contact with the probes in order to determine certain electric characteristics of the IC chip. Note that, if the wafer W has a size not greater than 8 inches, the wafer W is held substantially horizontal as shown in FIG. 7A when the main chuck 17 is driven upward excessively and the wafer W on the main chuck 17 is raised to the position indicated by a solid line from the position indicated by a broken line in FIG. 7A. Consequently, each of the probes 24A of the probe card 24 is resiliently moved up from the position indicated by a broken line to the position indicated by a solid line in FIG. 7A so that the tip of each of the probes moves from the starting point S to the terminal point E on the thick line in FIG. 7A. FIG. 7B shows the apparent horizontal movement of the tip from the starting point S to the terminal point E on the surface of the wafer W. However, since the tip of the probe is located within an electrode pad P of the IC chip, the probe 24A is held in electric contact with the electrode pad P. If, on the other hand, the wafer W has a larger size of, for example, 12 inches, the IC chip will have to be ultra-micro-machined and the electrode pads will probably be arranged at a smaller pitch. Then, the probe card will be provided with a correspondingly increased number of probes, which may be as many as 2,000. So, the load of all the probes 24A to be borne by the main chuck 17 will be very heavy and found somewhere between 10 kg and 20 kg. Then, as the wafer W is excessively raised from the position indicated by a broken line to the position indicated by a solid line in FIG. 8A, the shaft of the support (not shown) of the main chuck 17 will be bent and the wafer W will be tilted by, e.g., 20 to 30 .mu.m and moved outwardly to the position shown by solid lines in FIG. 8A. Consequently, each of the probes 24A of the probe card 24 is resiliently moved up from the position indicated by a broken line to the position indicated by a solid line in FIG. 8A so that the tip of each of the probes travels from the starting point S to the terminal point E on the thick line in FIG. 8A by a distance greater than its counterpart in FIG. 7A (as indicated by the arrow in FIG. 8B). Therefore, if the starting point S of the tip of the probe in FIG. 8A is identical with that of the probe in FIG. 7A, the terminal point E can be located out of the electrode pad P as shown in FIG. 8B. Then, no test signal will be transmitted from the probe 24A to the electrode pad P to damage the reliability of the test.